1. Field of the Invention
The present invention relates to a light emitting device, and more particularly to a chip-type package for high power III-V compound semiconductor light emitting diodes.
2. Description of the Prior Art
A first explanatory conventional chip-type light emitting diode (LED) device is disclosed in U.S. Pat. No. 6,345,903 B1. FIG. 1. herein shows a structure of the light emitting assembler 10 the patent disclosed. The LED 22 having an electrode formed on the bottom surface is adhered to a first metal contact 13 by silver paste or a solder layer 20. The other electrode of the LED chip 22 formed on the upper surface thereof is bonded to the other first metal electrode 14 by a conductive wire 23. Both of the first metal contacts 13, 14 are formed on an upper surface of a glass fiber substrate 12 and are connected to the second metal contacts 33, 34 on the bottom surface thereof by though holes 40, which have a conductive plating layer 41 formed thereon.
Enclosing each of the LED chips is a corresponding reflective frame 17 in a form of a reflective frame assembler. The reflective frame 17 has an inclined inner periphery surface in a conic form, which has the function to reflect the light emitted by the LED chip thereby causing the light to converge in an upward direction. A first transparent resin encapsulating layer 15 is then refilled the reflective frame 17 so as to protect the LED chip 22 and the conductive bonding wire 23.
Above the first resin encapsulator 15 is a second resin encapsulator 27 formed by injecting the resin into a mask mold 28 which has a plurality of semi-sphere concaves formed therein so as to form lens 29 for converging the light. After the resin encapsulator is cured, the mask mold 28 is then removed (not shown). Finally the LED assemble substrate is then saw from the cut line 42, which is along the center line of the through hole 40.
The surface mounted of the LED package in the first embodiment is for LED chip having two electrodes, respectively, on the upper and bottom surface. Thus, the light emitted is blocked by the upper electrode. Moreover, the base substrate 12 is an insulator, so that a through hold plating layer 41 is demanded to connect the first metal contacts 13, 14 on the upper surface and the second metal contacts 33, 34 on the bottom surface. The heat irradiated by the LED 22 can only be dissipated through the metal contacts 13, 33, and the through hole plating layer 41 since the LED 22, is encapsulated by resin 15. Consequently, bad heat dissipation capability of the substrate assembler is result.
The second explanatory conventional chip-type light emitting diode (LED) device is a flip-chip type disclosed in U.S. Pat. No. 6,396,082 B1, as shown in FIG. 2
The LED flip-chip 79 with a transparent substrate upward is fixed on a glass epoxy substrate 72, which has a through hole 75 formed therein directly above the LED chip 79 and two metal contacts 73, 74 on the upper surface 76a thereof extended to the lower surface 76b. The through hole 75 is filled with a transparent resin layer 77. Two metal electrodes 83, 84 on the upper surface of the LED 79 are respectively, bonded to the metal contacts 73, 74 by conductive wires 85, 86. The LED chip 79 and the conductive wires 85, 86 are then protected by a transparent sealing body 88. Finally, the glass epoxy substrate 72 is then upside down mounted onto a motherboard 91 by inserting the sealing body 88 into a hole 92 of the motherboard 91.
Since the LED is upside down and light irradiated is upward through the through hole 75 without blocking by any metal electrodes 83, 84, an excellent light emission efficiency is thus anticipated. However, owing to the insulating base substrate 72, the heat irradiated by the LED 79 can only be dissipated through the metal contacts 73, 74, since the LED 79, is encapsulated by resin 77 too. Consequently, heat dissipation capability of the substrate assembler as previous embodiment is result. The output power of LED is limited and a high power LED can""t be obtained without further improvement.
An object of the present invention is thus to propose a method and structure about surface mounting for a high power LED.
The present invention discloses two surface mount techniques for high power LED chips. In the first preferred embodiments, the LED chip having two electrodes formed on the same side is mounted onto an electric and thermal conductive substrate. The method comprises the following steps:
At first the base-substrate is cut or sawed or patterned to form a plurality of trenches. The trenches are then filled with spin on glass (SOG) or polyimide or BCB (B-staged bisbenzocyclobutene; BCB) layer. Thereafter, first metal contacts are formed on the upper surface of the base substrate. For every two metal contacts, respectively, at left hand side and right hand side of each trench function to support two electrodes of the LED chip. Next, the base-substrate is then back-side milling until at least the bottom of the trenches are exposed. Afterward, second metal contacts are formed on the milled surface. The second metal contacts on the right hand side and left hand side of each trench are formed for connecting external electrodes.
Subsequently, a reflective frame assembler is adhered to the upper surface of the base-substrate. The reflective frame assembler has a plurality of reflective frame, and each of them corresponding to a LED chip.
After that, the LED chip is up-side down placed within the reflective frame and with its p-type electrode and n-type electrode mounted on a pair of the first metal contacts with solder ball or solder layer. Finally, the LED chip is sealed and protected by transparent resin or epoxy. The upper portion of the reflective frame can be optionally formed with lens shaped so as to converge the light.
The method according to the second preferred embodiment is for LED chip with two electrodes, respectively, on the different sides of the LED.
The processes are as follows:
Firstly, the conductive base-substrate is formed with a plurality of trenches therein. The trenches are then filled with SOG or polyimide. Thereafter, first metal contacts are formed on the upper surface of the base substrate. It is noted that each two first metal contacts, one on the left hand side of the trench is for connecting a bottom electrode and the other one at the right hand side is for bonding a conductive wire. Hence, the metal contacts at left hand side and right hand side of each trench are not necessary to have equal area. Next, the base-substrate is then back-side milling until at least the bottom of the trenches are exposed. Afterward, second metal contacts are formed on the milled surface. The second metal contacts on the right hand side and left hand side of each trench are formed for connecting external electrodes.
Subsequently, a reflective frame assembler is adhered to the upper surface of the base-substrate. The reflective frame assembler has a plurality of reflective frame, and each of them corresponding to a LED chip. It is noted that the central position of the reflective frame is substantially aligned with one first metal contact, which is located at the central position of the reflective frame.
After that, the LED chip is placed within the reflective frame and with bottom electrode thereof attaching the first metal contact with solder ball or solder layer, wherein the first metal contact is approximately at the central position of the reflective frame.
Subsequently, a conductive wire is bonded to the upper electrode of the LED chip and the other first metal bonding electrode. Finally, the LED chip is sealed and protected by transparent resin or epoxy. The upper portion of the reflective frame can be optionally formed with lens shaped so as to converge the light.